In introduction of impurities using an ion-implanting apparatus, concentration and depth of implantation are easily controlled. For this reason, ion-implanting apparatuses are generally used in a step of introduction of impurities in production of semiconductor devices.
FIG. 10 is a sectional view of an essential part showing an example of a conventional ion-implanting apparatus. This drawing illustrates a high-current ion-implanting apparatus. In conventional ion-implanting apparatus 17, ion beam 2 is obtained by making a predetermined gas into plasma in ion source 1 and extracting ions with predetermined energy in the plasma from an extracting electrode. Desired ions are isolated from extracted ion beam 2 by mass spectrometry using mass spectrograph 3. Further, ions are completely isolated using splitting slit 4. Thereafter, the desired ions are accelerated to have final energy through accelerating electrode 5, and radiated onto an object to be processed, such as semiconductor wafer 7, disposed in implantation room 6. A beam current value of radiated ion beam 2 is measured by Faraday cup 8 to provide a quantity of impurities introduced.
FIG. 6 is a sectional view of an essential part showing an example of a conventional ion source. This drawing illustrates a Freeman type ion source. Ion source chamber 15 is formed of stainless steel, for example, into a cylindrical shape. Ion chamber 15 is approximately 300 mm in length and approximately 180 mm in diameter, for example. A flange portion at one end of ion source chamber 15 is fastened onto a body of ion-implanting apparatus 16 via bolts 18. A flange portion at another end of ion source chamber 15 is fastened to lid 20 by screws 19 via insulator 21 and a sealing member (not shown). This structure hermetically seals an interior of ion source chamber 15. Incidentally, filament 10 is provided inside of arc chamber 9. Gas supply nozzle 11 in communication with an interior of arc chamber 9 connects to gas source 12 via a gas passage including a mass flow controller and a valve. This structure allows supply of a dopant gas, such as arsine (AsH3), from gas supply nozzle 11 to the interior of arc chamber 9.
On a side of an ion extracting direction in arc chamber 9, ion outlet 13 is provided. In a position facing ion outlet 13, extracting electrode 14 is provided. Extracting electrode 14 has an ion through-hole 22. The ion through-hole is aligned with a center of the body of ion-implanting apparatus 16, in ion source chamber 15. Extracting electrode 14 is supported by ring-shaped base electrode 23 via electrically conductive struts. Base electrode 23 is supported by ground electrode 24 via insulating members, such as insulators. One end of ground electrode 24 is supported by a supporting post in intimate contact with a supporting hole provided in a sidewall of ion source chamber 15. Another end of ground electrode 24 is supported by supporting rod 26 that can project through the sidewall radially of ion source chamber 15. Extracting electrode 14 and base electrode 23 have the same electric potential, and are structured to be supported by ground electrode 24 via the insulating members.
During ion-implantation, a predetermined gas is introduced into arc chamber 9, and a predetermined high current is applied to filament 10 from a power source for generating thermal electrons. This current is a DC current of 150 A, for example. Further, a predetermined negative DC voltage of −100V, for example, is applied from a power source for generating arc discharge. Thus, discharge occurs between filament 10 and arc chamber 9, and a predetermined processing gas dissociates to generate plasma. At this time, a power source for extracting ions applies a predetermined high DC voltage of 80 kV, for example, across arc chamber 9 and extracting electrode 14. This extracts only positive ions in plasma generated in arc chamber 9 in a direction of extracting electrode 14 to form ion beam 2. A part where ion beam 2 passes is maintained at a vacuum of approximately 10−5 Torr, using a turbo-molecular pump or a cryopump.
Ion-implanting apparatuses supply ion beams 2 with high energy resolution. For this purpose, some ideas are considered to prevent fluctuations of voltage of extracting electrode 14 and an accelerating voltage of accelerating electrode 5, and keep these voltages constant. For example, in an ion-extracting power source for outputting a predetermined DC voltage to ion source 1 and extracting electrode 14, general commercial AC power is converted into desired DC power for use. AC components left after conversion, i.e. ripple components, cause variations in energy of ion beams 2. To address this problem, as shown in a technique of reducing ripple components in low energy injection disclosed in Japanese Patent Unexamined Publication H10-112277, maintaining high energy resolution is important.
As to ion source 1, a shape of ion outlet 13, a position of extracting electrode 14, gas flow and pressure supplied into arc chamber 9, current and voltage applied to filament 10, arc voltage, arc current, and magnetic field strength for trapping electrons inside of arc chamber 9 are optimized, according to a desired type of ions and extracting electrode. Additionally, according to implantation conditions, the shape of ion outlet 13 is changed or an extracting voltage is adjusted before ion beam 2 is set. Further, a device for changing a position of extracting electrode 14 to change a distance to ion outlet 13 is generally provided.